path: root/ipalib/plugins/dns.py

# Authors:
#   Pavel Zuna <pzuna@redhat.com>
#
# Copyright (C) 2010  Red Hat
# see file 'COPYING' for use and warranty information
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
"""
Domain Name System (DNS)

Manage DNS zone and resource records.

EXAMPLES:

 Add new zone:
   ipa dnszone-add example.com --name-server nameserver.example.com
                               --admin-email admin@example.com

 Add second nameserver for example.com:
   ipa dnsrecord-add example.com @ --ns-rec nameserver2.example.com

 Add a mail server for example.com:
   ipa dnsrecord-add example.com @ --mx-rec="10 mail2"

 Delete previously added nameserver from example.com:
   ipa dnsrecord-del example.com @ --ns-rec nameserver2.example.com

 Add new A record for www.example.com: (random IP)
   ipa dnsrecord-add example.com www --a-rec 80.142.15.2

 Add new PTR record for www.example.com
   ipa dnsrecord-add 15.142.80.in-addr.arpa 2 --ptr-rec www.example.com.

 Add new SRV records for LDAP servers. Three quarters of the requests
 should go to fast.example.com, one quarter to slow.example.com. If neither
 is available, switch to backup.example.com.
   ipa dnsrecord-add example.com _ldap._tcp --srv-rec="0 3 389 fast.example.com"
   ipa dnsrecord-add example.com _ldap._tcp --srv-rec="0 1 389 slow.example.com"
   ipa dnsrecord-add example.com _ldap._tcp --srv-rec="1 1 389 backup.example.com"

 Show zone example.com:
   ipa dnszone-show example.com

 Find zone with "example" in its domain name:
   ipa dnszone-find example

 Find records for resources with "www" in their name in zone example.com:
   ipa dnsrecord-find example.com www

 Find A records with value 10.10.0.1 in zone example.com
   ipa dnsrecord-find example.com --a-rec 10.10.0.1

 Show records for resource www in zone example.com
   ipa dnsrecord-show example.com www

 Delete zone example.com with all resource records:
   ipa dnszone-del example.com

 Resolve a host name to see if it exists (will add default IPA domain
 if one is not included):
   ipa dns-resolve www.example.com
   ipa dns-resolve www

"""

import netaddr
import time

from ipalib import api, errors, output
from ipalib import Command
from ipalib import Flag, Int, List, Str, StrEnum
from ipalib.plugins.baseldap import *
from ipalib import _, ngettext
from ipapython import dnsclient

# supported resource record types
_record_types = (
    u'A', u'AAAA', u'A6', u'AFSDB', u'APL', u'CERT', u'CNAME', u'DHCID', u'DLV',
    u'DNAME', u'DNSKEY', u'DS', u'HIP', u'IPSECKEY', u'KEY', u'KX', u'LOC',
    u'MX', u'NAPTR', u'NS', u'NSEC', u'NSEC3', u'NSEC3PARAM', u'PTR',
    u'RRSIG', u'RP', u'SIG', u'SPF', u'SRV', u'SSHFP', u'TA', u'TKEY',
    u'TSIG', u'TXT',
)

# attributes derived from record types
_record_attributes = [str('%srecord' % t.lower()) for t in _record_types]

# supported DNS classes, IN = internet, rest is almost never used
_record_classes = (u'IN', u'CS', u'CH', u'HS')

# normalizer for admin email
def _rname_normalizer(value):
    value = value.replace('@', '.')
    if not value.endswith('.'):
        value += '.'
    return value

def _create_zone_serial(**kwargs):
    """Generate serial number for zones."""
    return int('%s01' % time.strftime('%Y%d%m'))

def _validate_ipaddr(ugettext, ipaddr):
    try:
        ip = netaddr.IPAddress(ipaddr)
    except (netaddr.AddrFormatError, ValueError):
        return u'invalid address format'
    return None

def _validate_ipnet(ugettext, ipnet):
    try:
        net = netaddr.IPNetwork(ipnet)
    except (UnboundLocalError, ValueError):
        return u'invalid format'
    return None

def _validate_srv(ugettext, srv):
    try:
        prio, weight, port, host = srv.split()
    except ValueError:
        return u'format must be specified as "priority weight port target"'

    try:
        prio = int(prio)
        weight = int(weight)
        port = int(port)
    except ValueError:
        return u'the values of priority, weight and port must be integers'

    return None

def _validate_mx(ugettext, mx):
    try:
        prio, host = mx.split()
    except ValueError:
        return u'format must be specified as "priority mailserver"'

    try:
        prio = int(prio)
    except ValueError:
        return u'the value of priority must be integer'

    if prio < 0 or prio > 65535:
        return u'the value of priority must be between 0 and 65535'

    return None

def _validate_naptr(ugettext, naptr):
    "see RFC 2915 "
    try:
        order, pref, flags, svc, regexp, replacement = naptr.split()
    except ValueError:
        return u'format must be specified as "order preference flags service regexp replacement"'

    try:
        order = int(order)
        pref = int(pref)
    except ValueError:
        return u'order and preference must be integers'

    if order < 0 or order > 65535 or pref < 0 or pref > 65535:
        return u'the value of order and preference must be between 0 and 65535'

    flags = flags.replace('"','')
    flags = flags.replace('\'','')
    if len(flags) != 1:
        return u'flag must be a single character (quotation is allowed)'
    if flags.upper() not in "SAUP":
        return u'flag must be one of "S", "A", "U", or "P"'

    return None

_record_validators = {
    u'A': _validate_ipaddr,
    u'AAAA': _validate_ipaddr,
    u'APL': _validate_ipnet,
    u'SRV': _validate_srv,
    u'MX': _validate_mx,
    u'NAPTR': _validate_naptr,
}

def has_cli_options(entry, no_option_msg):
    entry = dict((t, entry.get(t, [])) for t in _record_attributes)
    numattr = reduce(lambda x,y: x+y,
                     map(lambda x: len(x), [ v for v in entry.values() if v is not None ]))
    if numattr == 0:
        raise errors.OptionError(no_option_msg)
    return entry

def is_ns_rec_resolvable(name):
    try:
        return api.Command['dns_resolve'](name)
    except errors.NotFound:
        raise errors.NotFound(
            reason=_('Nameserver \'%(host)s\' does not have a corresponding A/AAAA record') % {'host': name}
        )

def add_forward_record(zone, name, str_address):
    addr = netaddr.IPAddress(str_address)
    try:
        if addr.version == 4:
            api.Command['dnsrecord_add'](zone, name, arecord=str_address)
        elif addr.version == 6:
            api.Command['dnsrecord_add'](zone, name, aaaarecord=str_address)
        else:
            raise ValueError('Invalid address family')
    except errors.EmptyModlist:
        pass # the entry already exists and matches

def dns_container_exists(ldap):
    try:
        ldap.get_entry(api.env.container_dns, [])
    except errors.NotFound:
        return False
    return True

class dnszone(LDAPObject):
    """
    DNS Zone, container for resource records.
    """
    container_dn = api.env.container_dns
    object_name = 'DNS zone'
    object_name_plural = 'DNS zones'
    object_class = ['top', 'idnsrecord', 'idnszone']
    default_attributes = [
        'idnsname', 'idnszoneactive', 'idnssoamname', 'idnssoarname',
        'idnssoaserial', 'idnssoarefresh', 'idnssoaretry', 'idnssoaexpire',
        'idnssoaminimum'
    ] + _record_attributes
    label = _('DNS')

    takes_params = (
        Str('idnsname',
            cli_name='name',
            label=_('Zone name'),
            doc=_('Zone name (FQDN)'),
            normalizer=lambda value: value.lower(),
            primary_key=True,
        ),
        Str('idnssoamname',
            cli_name='name_server',
            label=_('Authoritative nameserver'),
            doc=_('Authoritative nameserver.'),
        ),
        Str('idnssoarname',
            cli_name='admin_email',
            label=_('Administrator e-mail address'),
            doc=_('Administrator e-mail address'),
            default_from=lambda idnsname: 'root.%s' % idnsname,
            normalizer=_rname_normalizer,
        ),
        Int('idnssoaserial?',
            cli_name='serial',
            label=_('SOA serial'),
            doc=_('SOA record serial number'),
            minvalue=1,
            create_default=_create_zone_serial,
            autofill=True,
        ),
        Int('idnssoarefresh?',
            cli_name='refresh',
            label=_('SOA refresh'),
            doc=_('SOA record refresh time'),
            minvalue=0,
            default=3600,
            autofill=True,
        ),
        Int('idnssoaretry?',
            cli_name='retry',
            label=_('SOA retry'),
            doc=_('SOA record retry time'),
            minvalue=0,
            default=900,
            autofill=True,
        ),
        Int('idnssoaexpire?',
            cli_name='expire',
            label=_('SOA expire'),
            doc=_('SOA record expire time'),
            default=1209600,
            minvalue=0,
            autofill=True,
        ),
        Int('idnssoaminimum?',
            cli_name='minimum',
            label=_('SOA minimum'),
            doc=_('How long should negative responses be cached'),
            default=3600,
            minvalue=0,
            maxvalue=10800,
            autofill=True,
        ),
        Int('dnsttl?',
            cli_name='ttl',
            label=_('SOA time to live'),
            doc=_('SOA record time to live'),
        ),
        StrEnum('dnsclass?',
            cli_name='class',
            label=_('SOA class'),
            doc=_('SOA record class'),
            values=_record_classes,
        ),
        Str('idnsupdatepolicy?',
            cli_name='update_policy',
            label=_('BIND update policy'),
            doc=_('BIND update policy'),
        ),
        Flag('idnszoneactive?',
            cli_name='zone_active',
            label=_('Active zone'),
            doc=_('Is zone active?'),
            flags=['no_create', 'no_update'],
            attribute=True,
        ),
        Flag('idnsallowdynupdate',
            cli_name='allow_dynupdate',
            label=_('Dynamic update'),
            doc=_('Allow dynamic updates.'),
            attribute=True,
        ),
    )

api.register(dnszone)


class dnszone_add(LDAPCreate):
    """
    Create new DNS zone (SOA record).
    """
    takes_options = LDAPCreate.takes_options + (
        Flag('force',
             doc=_('Force DNS zone creation even if nameserver not in DNS.'),
        ),
        Str('ip_address?', _validate_ipaddr,
            doc=_('Add the nameserver to DNS with this IP address'),
        ),
    )

    def pre_callback(self, ldap, dn, entry_attrs, *keys, **options):
        if not dns_container_exists(self.api.Backend.ldap2):
            raise errors.NotFound(reason=_('DNS is not configured'))

        entry_attrs['idnszoneactive'] = 'TRUE'
        entry_attrs['idnsallowdynupdate'] = str(
            entry_attrs.get('idnsallowdynupdate', False)
        ).upper()

        # Check nameserver has a forward record
        nameserver = entry_attrs['idnssoamname']

        if not 'ip_address' in options and not options['force']:
            is_ns_rec_resolvable(nameserver)

        if nameserver[-1] != '.':
            nameserver += '.'

        entry_attrs['nsrecord'] = nameserver
        entry_attrs['idnssoamname'] = nameserver
        return dn

    def post_callback(self, ldap, dn, entry_attrs, *keys, **options):
        if 'ip_address' in options:
            nameserver = entry_attrs['idnssoamname'][0][:-1] # ends with a dot
            nsparts = nameserver.split('.')
            add_forward_record('.'.join(nsparts[1:]),
                               nsparts[0],
                               options['ip_address'])

        return dn

api.register(dnszone_add)


class dnszone_del(LDAPDelete):
    """
    Delete DNS zone (SOA record).
    """

api.register(dnszone_del)


class dnszone_mod(LDAPUpdate):
    """
    Modify DNS zone (SOA record).
    """
    def pre_callback(self, ldap, dn, entry_attrs, *keys, **options):
        entry_attrs['idnsallowdynupdate'] = str(
            entry_attrs.get('idnsallowdynupdate', False)
        ).upper()
        return dn

api.register(dnszone_mod)


class dnszone_find(LDAPSearch):
    """
    Search for DNS zones (SOA records).
    """

api.register(dnszone_find)


class dnszone_show(LDAPRetrieve):
    """
    Display information about a DNS zone (SOA record).
    """

api.register(dnszone_show)


class dnszone_disable(LDAPQuery):
    """
    Disable DNS Zone.
    """
    has_output = output.standard_value
    msg_summary = _('Disabled DNS zone "%(value)s"')

    def execute(self, *keys, **options):
        ldap = self.obj.backend

        dn = self.obj.get_dn(*keys, **options)

        try:
            ldap.update_entry(dn, {'idnszoneactive': 'FALSE'})
        except errors.EmptyModlist:
            pass

        return dict(result=True, value=keys[-1])

api.register(dnszone_disable)


class dnszone_enable(LDAPQuery):
    """
    Enable DNS Zone.
    """
    has_output = output.standard_value
    msg_summary = _('Enabled DNS zone "%(value)s"')

    def execute(self, *keys, **options):
        ldap = self.obj.backend

        dn = self.obj.get_dn(*keys, **options)

        try:
            ldap.update_entry(dn, {'idnszoneactive': 'TRUE'})
        except errors.EmptyModlist:
            pass

        return dict(result=True, value=keys[-1])

api.register(dnszone_enable)


class dnsrecord(LDAPObject):
    """
    DNS record.
    """
    parent_object = 'dnszone'
    container_dn = api.env.container_dns
    object_name = 'DNS resource record'
    object_name_plural = 'DNS resource records'
    object_class = ['top', 'idnsrecord']
    default_attributes = _record_attributes + ['idnsname']

    label = _('DNS resource record')

    takes_params = (
        Str('idnsname',
            cli_name='name',
            label=_('Record name'),
            doc=_('Record name'),
            primary_key=True,
        ),
        Int('dnsttl?',
            cli_name='ttl',
            label=_('Time to live'),
            doc=_('Time to live'),
        ),
        StrEnum('dnsclass?',
            cli_name='class',
            label=_('Class'),
            doc=_('DNS class'),
            values=_record_classes,
        ),
    )

    def is_pkey_zone_record(self, *keys):
        idnsname = keys[-1]
        if idnsname == '@' or idnsname == ('%s.' % keys[-2]):
            return True
        return False

    def get_dn(self, *keys, **options):
        if self.is_pkey_zone_record(*keys):
            return self.api.Object[self.parent_object].get_dn(*keys[:-1], **options)
        return super(dnsrecord, self).get_dn(*keys, **options)

    def attr_to_cli(self, attr):
        try:
            cliname = attr[:-len('record')].upper()
        except IndexError:
            cliname = attr
        return cliname

api.register(dnsrecord)


class dnsrecord_cmd_w_record_options(Command):
    """
    Base class for DNS record commands with record options.
    """
    record_param_doc = 'comma-separated list of %s records'

    def get_record_options(self):
        for t in _record_types:
            t = t.encode('utf-8')
            doc = self.record_param_doc % t
            validator = _record_validators.get(t)
            if validator:
                yield List(
                    '%srecord?' % t.lower(), validator,
                    cli_name='%s_rec' % t.lower(), doc=doc,
                    label='%s record' % t, attribute=True
                )
            else:
                yield List(
                    '%srecord?' % t.lower(), cli_name='%s_rec' % t.lower(),
                    doc=doc, label='%s record' % t, attribute=True
                )

    def record_options_2_entry(self, **options):
        entries = dict((t, options.get(t, [])) for t in _record_attributes)
        entries.update(dict((k, []) for (k,v) in entries.iteritems() if v == None ))
        return entries


class dnsrecord_mod_record(LDAPQuery, dnsrecord_cmd_w_record_options):
    """
    Base class for adding/removing records from DNS resource entries.
    """
    has_output = output.standard_entry

    def get_options(self):
        for option in super(dnsrecord_mod_record, self).get_options():
            yield option
        for option in self.get_record_options():
            yield option

    def execute(self, *keys, **options):
        ldap = self.obj.backend

        dn = self.obj.get_dn(*keys, **options)

        entry_attrs = self.record_options_2_entry(**options)

        dn = self.pre_callback(ldap, dn, entry_attrs, *keys, **options)

        try:
            (dn, old_entry_attrs) = ldap.get_entry(dn, entry_attrs.keys())
        except errors.NotFound:
            self.obj.handle_not_found(*keys)

        self.update_old_entry_callback(entry_attrs, old_entry_attrs)

        try:
            ldap.update_entry(dn, old_entry_attrs)
        except errors.EmptyModlist:
            pass

        if options.get('all', False):
            attrs_list = ['*']
        else:
            attrs_list = list(
                set(self.obj.default_attributes + entry_attrs.keys())
            )

        try:
            (dn, entry_attrs) = ldap.get_entry(dn, attrs_list)
        except errors.NotFound:
            self.obj.handle_not_found(*keys)

        if self.obj.is_pkey_zone_record(*keys):
            entry_attrs[self.obj.primary_key.name] = [u'@']

        retval = self.post_callback(keys, entry_attrs)
        if retval:
            return retval

        return dict(result=entry_attrs, value=keys[-1])

    def update_old_entry_callback(self, entry_attrs, old_entry_attrs):
        pass

    def pre_callback(self, ldap, dn, entry_attrs, *keys, **options):
        return dn

    def post_callback(self, keys, entry_attrs):
        pass


class dnsrecord_add_record(dnsrecord_mod_record):
    """
    Add records to DNS resource.
    """
    NO_CLI = True

    def update_old_entry_callback(self, entry_attrs, old_entry_attrs):
        for (a, v) in entry_attrs.iteritems():
            if not isinstance(v, (list, tuple)):
                v = [v]
            old_entry_attrs.setdefault(a, [])
            old_entry_attrs[a] += v

api.register(dnsrecord_add_record)


class dnsrecord_add(LDAPCreate, dnsrecord_cmd_w_record_options):
    """
    Add new DNS resource record.
    """
    no_option_msg = 'No options to add a specific record provided.'
    takes_options = LDAPCreate.takes_options + (
        Flag('force',
             flags=['no_option', 'no_output'],
             doc=_('force NS record creation even if its hostname is not in DNS'),
        ),
    )

    def get_options(self):
        for option in super(dnsrecord_add, self).get_options():
            yield option
        for option in self.get_record_options():
            yield option

    def args_options_2_entry(self, *keys, **options):
        has_cli_options(options, self.no_option_msg)
        return super(dnsrecord_add, self).args_options_2_entry(*keys, **options)

    def _nsrecord_pre_callback(self, ldap, dn, entry_attrs, *keys, **options):
        if options.get('force', False):
            return dn

        for ns in options['nsrecord']:
            is_ns_rec_resolvable(ns)
        return dn

    def _ptrrecord_pre_callback(self, ldap, dn, entry_attrs, *keys, **options):
        components = dn.split(',',2)
        addr = components[0].split('=')[1]
        zone = components[1].split('=')[1]
        if zone.find('ip6') != -1:
            zone = zone.replace('.ip6.arpa.','')
            zone_len = 32
        else:
            zone = zone.replace('.in-addr.arpa.','')
            zone_len = 4

        if len(addr.split('.'))+len(zone.split('.')) != zone_len:
            raise errors.ValidationError(name='cn', error=unicode('IP address must have exactly '+str(zone_len)+' components'))

        return dn

    def pre_callback(self, ldap, dn, entry_attrs, *keys, **options):
        for rtype in options:
            rtype_cb = '_%s_pre_callback' % rtype
            if hasattr(self, rtype_cb):
                dn = getattr(self, rtype_cb)(ldap, dn, entry_attrs, *keys, **options)

        return dn

    def exc_callback(self, keys, options, exc, call_func, *call_args, **call_kwargs):
        if call_func.func_name == 'add_entry':
            if isinstance(exc, errors.DuplicateEntry):
                self.obj.methods.add_record(
                    *keys, **self.record_options_2_entry(**options)
                )
                return
        raise exc

api.register(dnsrecord_add)


class dnsrecord_delentry(LDAPDelete):
    """
    Delete DNS record entry.
    """
    msg_summary = _('Deleted record "%(value)s"')
    NO_CLI = True

api.register(dnsrecord_delentry)


class dnsrecord_del(dnsrecord_mod_record):
    """
    Delete DNS resource record.
    """
    no_option_msg = 'Neither --del-all nor options to delete a specific record provided.'
    takes_options = (
            Flag('del_all',
                default=False,
                label=_('Delete all associated records'),
            ),
    )

    def execute(self, *keys, **options):
        if options.get('del_all', False):
            return self.obj.methods.delentry(*keys)

        return super(dnsrecord_del, self).execute(*keys, **options)

    def record_options_2_entry(self, **options):
        entry = super(dnsrecord_del, self).record_options_2_entry(**options)
        return has_cli_options(entry, self.no_option_msg)

    def update_old_entry_callback(self, entry_attrs, old_entry_attrs):
        for (a, v) in entry_attrs.iteritems():
            if not isinstance(v, (list, tuple)):
                v = [v]
            for val in v:
                try:
                    old_entry_attrs[a].remove(val)
                except (KeyError, ValueError):
                    raise errors.NotFound(reason='%s record with value %s not found' %
                                          (self.obj.attr_to_cli(a), val))

    def post_callback(self, keys, entry_attrs):
        if not self.obj.is_pkey_zone_record(*keys):
            for a in _record_attributes:
                if a in entry_attrs and entry_attrs[a]:
                    return
            return self.obj.methods.delentry(*keys)

api.register(dnsrecord_del)


class dnsrecord_show(LDAPRetrieve, dnsrecord_cmd_w_record_options):
    """
    Display DNS resource.
    """
    def has_output_params(self):
        for option in self.get_record_options():
            yield option

    def post_callback(self, ldap, dn, entry_attrs, *keys, **options):
        if self.obj.is_pkey_zone_record(*keys):
            entry_attrs[self.obj.primary_key.name] = [u'@']
        return dn

api.register(dnsrecord_show)


class dnsrecord_find(LDAPSearch, dnsrecord_cmd_w_record_options):
    """
    Search for DNS resources.
    """
    def get_options(self):
        for option in super(dnsrecord_find, self).get_options():
            yield option
        for option in self.get_record_options():
            yield option.clone(query=True)

    def pre_callback(self, ldap, filter, attrs_list, base_dn, scope, *args, **options):
        record_attrs = self.record_options_2_entry(**options)
        record_filter = ldap.make_filter(record_attrs, rules=ldap.MATCH_ALL)
        filter = ldap.combine_filters(
            (filter, record_filter), rules=ldap.MATCH_ALL
        )
        return (filter, base_dn, ldap.SCOPE_SUBTREE)

    def post_callback(self, ldap, entries, truncated, *args, **options):
        if entries:
            zone_obj = self.api.Object[self.obj.parent_object]
            zone_dn = zone_obj.get_dn(args[0])
            if entries[0][0] == zone_dn:
                entries[0][1][zone_obj.primary_key.name] = [u'@']

api.register(dnsrecord_find)

class dns_resolve(Command):
    """
    Resolve a host name in DNS
    """
    has_output = output.standard_value
    msg_summary = _('Found \'%(value)s\'')

    takes_args = (
        Str('hostname',
            label=_('Hostname'),
        ),
    )

    def execute(self, *args, **options):
        query=args[0]
        if query.find(api.env.domain) == -1 and query.find('.') == -1:
            query = '%s.%s.' % (query, api.env.domain)
        if query[-1] != '.':
            query = query + '.'
        reca = dnsclient.query(query, dnsclient.DNS_C_IN, dnsclient.DNS_T_A)
        rec6 = dnsclient.query(query, dnsclient.DNS_C_IN, dnsclient.DNS_T_AAAA)
        records = reca + rec6
        found = False
        for rec in records:
            if rec.dns_type == dnsclient.DNS_T_A or \
              rec.dns_type == dnsclient.DNS_T_AAAA:
                found = True
                break

        if not found:
            raise errors.NotFound(
                reason=_('Host \'%(host)s\' not found') % {'host': query}
            )

        return dict(result=True, value=query)

api.register(dns_resolve)

class dns_is_enabled(Command):
    """
    Checks if any of the servers has the DNS service enabled.
    """
    NO_CLI = True
    has_output = output.standard_value

    base_dn = 'cn=masters,cn=ipa,cn=etc,%s' % api.env.basedn
    filter = '(&(objectClass=ipaConfigObject)(cn=DNS))'

    def execute(self, *args, **options):
        ldap = self.api.Backend.ldap2
        dns_enabled = False

        try:
            ent = ldap.find_entries(filter=self.filter, base_dn=self.base_dn)
            if len(ent):
                dns_enabled = True
        except Exception, e:
            pass

        return dict(result=dns_enabled, value=u'')

api.register(dns_is_enabled)